Many products, such as electronic devices, medical devices and pharmaceuticals, are sensitive to water vapor and ambient gases, and exposure to them causes product deterioration and/or product performance degradation. Consequently, blocking coatings are commonly used as a protective measure to safeguard against such undesired exposure.
Plastic coating or layers are frequently used as blocking coatings. Unfortunately, they suffer from poor gas and liquid permeation resistance, which have values that are typically several orders of magnitude below the requisite value of permeation resistance for acceptable product performance. By way of example, certain LED display and solar cell encapsulation applications require water vapor transmission on the order of <10−4 grams/square meter/day, and in contrast, the water vapor transmission rate for Polyethylene Terephthalate (PET), a commonly used plastic substrate, is in the order of between about 1 and about 10 grams/square meter/day. Those skilled in the art will recognize that water vapor transmission can be thought of as being inversely proportional to water permeation resistance.
Other approaches protect against exposure to undesired elements by applying a blocking coating to plastic films like PET, to reduce water vapor permeability. These coatings are typically single layers of inorganic materials like Al, SiOx, AlOx and Si3N4, deposited onto the plastic substrates using well-known vacuum deposition processes. A single layer coating of these inorganic materials typically will reduce the water vapor permeability of PET from 1.0 to 0.1 grams/square meter/day. Thus, single blocking coating on a plastic substrate also fails to meet a requisite value of permeation resistance.
FIG. 1 shows a dyad 10, which refers to a structure that is formed when an inorganic blocking layer or coating 12 is formed atop an organic layer 14 (e.g., acrylic). Dyad 10 may be deposited as a protective layer on a polymeric substrate. Blocking layer 12 consists of densely packed oxide particles and acts as a conventional diffusive barrier, hindering gas and moisture permeation through it. Commonly found defects in a blocking layer, however, allow moisture and ambient gas molecules to diffuse through the oxide particles, and ultimately degrade the underlying electronic devices, such as solar cells and organic light emitting diodes. To overcome the drawbacks associated with the presence of these defects, organic layer 14 is applied to blocking layer 12 as an attempt to smooth defects and the underlying surface of polymeric substrate. Certain other approaches deposit multiple dyads on polymeric substrates serving the predicate that non-aligned defects present in multiple dyads further reduce gas and moisture permeation. However, depositing multiple dyads leads to more expensive barriers as well as reduces the flexibility of the final barrier film.
Regardless of whether a single layer of blocking coating or a single dyad or multiple dyads are used as a protective measure, conventional diffusion retarding schemes described above fail to protect an underlying polymeric layer to the requisite extent for a particular application (e.g., solar cell application and LED display application). Specifically, the defects present in the inorganic layer are not effectively filled-in and provide a diffusion pathway for moisture and undesired ambient gases to travel from the surface of the blocking layer to the polymer substrate. Conventional polymeric substrates are not able to adequately protect the underlying product that it encapsulates from exposure to moisture and undesired ambient gases. As a result, the underlying product degrades over time, eventually failing and suffering from a relatively shorter life span.
What is, therefore, needed are novel protective layer designs that effectively protect underlying moisture and gas sensitive products from moisture and undesired ambient gases, and that do not suffer from the drawbacks encountered by conventional designs of blocking layer and dyads.